add setup.py to compile c extension

Author: SimonBlanke

setup.py

@@ -0,0 +1,43 @@
+"""Build configuration for optional C extension.
+
+The C extension provides accelerated array operations for the pure Python
+backend. If compilation fails (no C compiler), the package installs
+normally and falls back to pure Python.
+"""
+
+import os
+
+from setuptools import Extension, setup
+from setuptools.command.build_ext import build_ext
+
+_c_source = os.path.join(
+    "src",
+    "gradient_free_optimizers",
+    "_array_backend",
+    "_fast_ops.c",
+)
+
+
+class OptionalBuildExt(build_ext):
+    """Build C extensions, silently skip on failure."""
+
+    def build_extension(self, ext):  # noqa: D102
+        try:
+            super().build_extension(ext)
+        except Exception as e:
+            print(
+                f"WARNING: Could not build C extension '{ext.name}': {e}\n"
+                f"Falling back to pure Python array backend."
+            )
+
+
+setup(
+    cmdclass={"build_ext": OptionalBuildExt},
+    ext_modules=[
+        Extension(
+            "gradient_free_optimizers._array_backend._fast_ops",
+            sources=[_c_source],
+            extra_compile_args=["-O2"],
+        ),
+    ],
+)